Miscibility of poly(3-chloropropyl methacrylate) with various polymethacrylates

Eur. Polym. J. Vol. 29, No. 7, pp. 909-912, 1993 Printed in Great Britain. All rights reserved

0014-3057/93 $6.00 + 0.00 Copyright © 1993 Pergamon Press Ltd

MISCIBILITY OF POLY(3-CHLOROPROPYL METHACRYLATE) WITH VARIOUS POLYMETHACRYLATES S. M. Low, S. Y. LEE and S. H. GOH* Department of Chemistry, National University of Singapore, Singapore 0511, Republic of Singapore (Received 28 September 1992)

A~traet--The miscibility of poly(3-chloropropyl methacrylate) (PCPMA) with various polymethacrylates was studied by differential scanning calorimetry. PCPMA is miscible with poly(tetrahydrofurfuryl methacrylate) but immiscible with polymers of methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate and cyclohexyl methacrylate. As compared with poly(chloromethyl methacrylate) and poly(2-chloroethyl methacrylate), PCPMA has a poorer miscibility with polymethacrylates.

INTRODUCTION

The miscibility of a polymethacrylate generally decreases with increasing size of its pendant group [I-7]. Lower members of the polymethacrylates are more readily miscible with other polymers. It is also known that polymethacrylates are mutually immiscible with each other [2]. For example, poly(methyl methacrylate) ( P M M A ) is immiscible with poly(ethyl methacrylate) ( P E M A ) and poly(n-propyl methacrylate) (PnPMA). Our recent studies have shown that poly(chloromethyl methacrylate) ( P C M M A ) and poly(2-chloroethyl methacrylate) ( P C E M A ) are miscible with several polymethacrylates [5, 6]. In this respect, the two chlorine-containing polymethacrylates behave like poly(vinyl chloride) (PVC) which is miscible with some polymethacrylates [1,7]. Our studies have also shown that the miscibility range of P C E M A with polymethacrylates is narrower than that of P C M M A . In this communication, we report the miscibility of poly(3-chloropropyl methacrylate) ( P C P M A ) with various polymethacrylates.

2 ml conc. H2SO4, with subsequent neutralizing with a 5% K2CO 3 solution, washing with H 2 0 , and drying over anhydrous Na2 SO4. The dried organic layer was concentrated at reduced pressure and the residue was distilled at 61-62°/2 mm Hg to yield 23.7 g (81%) of CPMA. i.r.: 1713 cm -1 (C----O), 1638 (C----C). IH-NMR (CDCI3): 6 = 1.95ppm (s, --CH3), 2.20 (t, ---CH2--), 3.55 (t, --CH2CI), 4.25 (t, ---O--CH2--), 5.60 (s, - - C H = ) and 6.05 (s, --CH----). Analysis for CTHNC102: calcd: C 51.7%; H 6.8%; C1 21.8%. Found: C 51.5%; H 7.0%; CI 21.8%. CPMA was polymerized in 2-butanone at reflux temperature of 6 hr using 0.25% by weight of azobisisobutyronitrile as initiator. The polymer PCPMA was obtained by precipitation of the solution in excess methanol. The main characteristics of polymethacrylates used in this study are given in Table 1. Polymer blends

Blends of PCPMA with various polymethacrylates were prepared by solution casting from tetrahydrofuran (THF). THF was allowed to evaporate slowly at room temperature for 1-2 days. The cast films were then dried in vaeuo at 90 ° for 4 days.

CH 3

Tg measurements

---CH2---~--

R = --CH2CI

PCMMA

= ---CH2 CH2C1

PCEMA

= --CH2CH2CH2CI

PCPMA

EXPERIMENTAL PROCEDURES

Materials

The glass transition temperatures (TBs) of various samples were measured with a Du Pont 2910 differential scanning calorimeter using a heating rate of 20°/min. Ts was taken as the initial onset of the change of slope in the DSC curve. The reported Tg is the average value based on the second and subsequent runs. Cloud point measurements

All the miscible blends were examined for the existence of lower critical solution temperature (LCST) using the method described previously [5]. The temperature at which the film first showed cloudiness was taken as the cloud point.

Monomeric CPMA was prepared by esterification of methacrylic acid with 3-chloro-l-propanol. A mixture of 15.5g of methacrylic acid (0.18tool) and 17.2g of HOCH2CH2CH2C! (0.18 tool) was refluxed in 200 ml benzene for 6 hr in the presence of 0.50 g hydroquinone and

RESULTS AND DISCUSSION

P C P M A / P M M A blends

All the blends were transparent and remained so upon heating to 280 °. However, D S C measurements showed the existence of two Tgs in each blend. The Tg values correspond to those of P C P M A and

*To whom all correspondence should be addressed. 909

S. M. Low et al.

910

Polymer Poly(methylmethacrylate) Poly(ethylmethacrylate) Poly(n-propylmethacrylate) Poly(isopropylmethacrylate) Poly(n-butylmethacrylate) Poly(tetrahydrofurfuryl methacrylate) Poly(cyclohexylmethacrylate) Poly(3-chloropropylmethacrylate) *[n]= 0.33dl/g in 2-butanoneat 30°.

Table I. Characteristicsof polymethacrylates Abbreviation Source Du Pont (Elvacite2010) PMMA PEMA Du Pont (Elvacite2042) ScientificPolymerProducts PnPMA PiPMA ScientificPolymerProducts PnBMA Du Pont (Elvacite2044) PTHFMA ScientificPolymerProducts ScientificPolymerProducts PCHMA This Laboratory PCPMA

PMMA, indicating that PCPMA is immiscible with PMMA. A typical DSC curve is shown in Fig. 1. The transparency of the blends is likely due to the matching of the refractive indices of the two polymers. The refractive index of PMMA is 1.490 [8] and that of PCPMA is estimated to be 1.489 using the Vogel method [9]. P C P M A / P E M A blends

The blends were transparent and turned cloudy when heated to 165-170 °, suggesting the existence of LCST behavior. However, DSC measurements showed the existence of two Tss in each blend, indicating immiscibility. A typical DSC curve is shown in Fig. 1. The clarity of the blends is also likely due to the matching of the refractive indices of PEMA (n = 1.485) [8] and PCPMA. The development of cloudiness is then a result of different temperature dependence of the refractive indices of the two polymers. The blends are judged to be immiscible based on the single Ts criterion for miscibility. P C P M A / P T H F M A blends

Molwt (Mw) 120,000 310,000 175,000 * 288,000 240,000 66,000 138,000

Ti(°) 100 65 45 82 20 57 95 52

and PTHFMA (n = 1.5096) [8] is larger than those between PCPMA and other polymethacrylates. The clarity of the blends may then be an indication of miscibility. Due to the close proximity of the Ts values of the two components (ATs g 5°), it is difficult to ascertain the miscibility of the blends by conventional Ts measurements. For a blend of two polymers with close Ts values, the enthalpy recovery peak of an annealed blend can be used to ascertain its miscibility [10, 11]. A single enthalpy recovery peak is indicative of a miscible blend. A 1:1 physical mixture of PCPMA and PTHFMA was heated to 70° and kept at that temperature for 20 min, followed by annealing at 40 ° for 14 days. As shown in Fig. 2, the annealed mixture showed two distinct enthalpy recovery peaks, indicating the applicability of the method to ascertain the miscibility of PCPMA/PTHFMA blends. Various blends were similarly annealed and the DSC curves of the annealed blends are also shown in Fig. 2. Each annealed sample showed a single enthalpy recovery peak, which moved progressively to higher temperature with increasing PTHFMA content. Thus, PCPMA is judged to be miscible with PTHFMA.

All the blends were transparent and remained so on heating to 285 ° where discoloration began to develop. The difference in refractive indices between PCPMA

6

..--- 6

t

O

0

~D

J

o

5 4 3

5

2

1

J 0

I 40

I I 80 120 Temperature (°C)

O

I 160

Fig. I. DSC curves for various PCPMA/polymethacrylate (50/50) blends. 1, PMMA; 2, PEMA; 3, PiPMA; 4, PnBMA; 5, PCHMA; and 6, PCMMA/PCHMA blend.

~ 20

I 40

I I 60 80 Temperature (°C)

I 100

Fig. 2. DSC curves for annealed PCPMA/P'rHFMA blends. Wt% PCPMA in blend: 1, 10; 2, 25; 3, 50; 4, 75; 5, 9t); and 6, physical mixture (50/50).

Miscibility of PCPMA with various polymethacrylates

PCPMA /PnPMA blends The blends had good clarity which may be due to the matching of the refractive indices of PnPMA (n = 1.484) [8] and PCPMA. The Tg values of the two polymers are close. The enthalpy recovery method is not useful in ascertaining the miscibility of the blends as an annealed physical mixture of the two polymers shows only one enthalpy recovery peak. However, in view of the immiscibility of PCPMA with PMMA, PEMA and PiPMA, it is likely that PCPMA is also immiscible with PnPMA.

PCPMA/PiPMA and PCPMA/PnBMA blends All the blends were hazy. DSC measurements showed the existence of two Tgs in each blend, and the values are close to those of the two component polymers. It is concluded that PCPMA is immiscible with both PiPMA and PnBMA.

PCPMA/PCHMA and PCMMA/PCHMA blends The good clarity of the blends may arise from the small difference in refractive indices between PCPMA and P C H M A (n = 1.507) [8]. However~ DSC measurements showed the existence of two Tgs in each blend, indicating the immiscibility of PCPMA with PCHMA. Since the earlier work did not study the miscibility behaviour of P C M M A with PCHMA, we also examined the miscibility of P C M M A / P C H M A blends. DSC measurements showed the existence of two Tgs in each blend. The Tg values correspond to those of P C M M A and PCHMA. A typical DSC curve is shown in Fig. 1. It is concluded that P C M M A is immiscible with PCHMA.

Miscibility behaviour Table 2 summarizes the miscibility of PCMMA, PCEMA and PCPMA with various polymethacrylates. The results clearly demonstrate that the ability of a chlorine-containing polymethacrylate to be miscible with polymethacrylates decreases in the order P C M M A > PCEMA > PCPMA. The miscibility of PVC-containing blends is generally attributed to hydrogen-bonding interactions involving the cthydrogen atoms of PVC and the proton-accepting groups of the other polymer [13, 14]. For a chlorinecontaining polymethacrylate, the presence of electron-withdrawing chlorine and the ester carboxyl group makes the hydrogen atoms of the CH 2C1 group acidic, and the acidity decreases in the order P C M M A > PCEMA > PCPMA because of the intervening methylene groups. Thus, the differences in the acidity of CH2CI hydrogen atoms may account for the different miscibility ranges of the three chlorine-containing polymethacrylates with various polymethacrylates. Table 2. Miscibility behaviour of blends PCMMA

PMMA PEMA PnPMA PiPMA PnBMA PCHMA PTHFMA

Miscible Miscible Miscible Miscible Immiscible Immiscible Miscible

PCEMA

Miscible Miscible Immiscible Immiscible Immiscible Immiscible Miscible

PCPMA

Immiscible Immiscible Immiscible Immiscible Immiscible Immiscible Miscible

911

Another notable point is the good miscibility of P T H F M A which is miscible with the three chlorinecontaining polymers. In another study, we also observed that poly(2-bromoethyl methacrylate) (PBEMA) is miscible with P T H F M A but is immiscible with other polymethacrylates [11]. In contrast, PCHMA, which is structurally quite similar to P T H F M A but without ether oxygen atoms in the pendant groups, is immiscible with the three chlorinecontaining polymethacrylates and also with PBEMA. Apparently, the presence of additional moieties, i.e. the ether oxygen atoms, in P T H F M A plays an important role in its good miscibility. Coleman and coworkers [15, 16] have recently proposed a general guide to polymer miscibility based on a non-hydrogen-bonded solubility parameter (6nh) approach. The closer the 6,h values of the two polymers and the stronger the intermolecular interactions, the greater is the probability of miscibility. The miscibility of PVC with polymethacrylates has been explained by this approach [15, 16]. The 6,h values of polymethacrylates decrease from 18.4 (J/cm3) 1/2 for P M M A to 17.5 (J/crn3) 1/2 for poly(nhexyl methacrylate). The difference in 6*h values between PVC (20.2 (J/cm3) 1/2) and a polymethacrylate becomes larger with increasing number of methylene unit in the pendant group. Thus, miscibility between PVC and higher members of polymethacrylates is not favoured. The 6nh values for PCMMA, PCEMA and PCPMA are 20.7, 20.0 and 19.6 (J/cm3) ~/2, respectively. From these 6~h values alone, PCPMA is expected to show a wider miscibility range with polymethacrylates. However, Coleman and coworkers have pointed out that a weaker intermolecular interaction requires a more closely matched 6~h values. As pointed out earlier, the intensity of intermolecular interactions decreases in the order P C M M A > P C E M A > PCPMA. Therefore, PCPMA is likely to be miscible with other polymethacrylates. It is of interest to note that 6~h for P T H F M A is estimated as 19.4 (J/em3) ~/2 which is very close to that of PCPMA. Accordingly, PCPMA is expected to be miscible with P T H F M A based on the 6nh approach.

Acknowledgement--Financial support of this research by the National University of Singapore is gratefully acknowledged.

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