Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-04-22
2003-11-25
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C525S222000
Reexamination Certificate
active
06653405
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to blends of acrylate polymers and more particularly to acrylate polymer blends having a high heat distortion temperature and to ingredients for preparing such blends.
2. Brief Description of the Prior Art
Polymers of acrylate and methacrylate esters have come to be used widely in applications wherein optical clarity is a highly desired property. They are readily prepared in sheets of various thicknesses and can be formed at elevated temperatures into shapes that are useful as housings for lamps and the like.
However, their relatively low glass transition temperature causes them to soften and lose strength at relatively low temperatures and thus limits their use for applications in which they may be subjected to temperatures above their heat distortion temperature.
Among the acrylate ester polymers, poly(methyl methacrylate) (PMMA) is the material most widely used for glazing, clear transparent housings, and the like. Although poly(methyl methacrylate) is well known for its excellent weathering, clarity and resistance to ultraviolet light, it suffers from a relatively low softening point (85° C. to 105° C.), especially when compared to Bisphenol A polycarbonate resins, which have a softening point in the range of 135° C. to 150° C. Because of its lower softening point, PMMA is limited in its applications where high temperature is involved, e.g., lamp housings and the like. Consequently, designers cannot take advantage of the other appealing characteristics of PMMA, such as clarity and UV resistance. Given the relatively low thermal performance of typical PMMA polymers and even lower thermal performance of impact modified acrylic polymers, some attempts have been made to tailor the thermal performance of either polymer to a specific range, preferably while maintaining the high light transmission and UV resistance of the base PMMA polymer.
Typically, for random copolymers the polarity and the stiffness of the polymer chain is the average of the values for the individual respective homopolymers. (Rodriguez, F.; Principles of Polymer Systems; Hemisphere Publishing; New York; 1989; pp 49). Gordon and Taylor developed an empirical relationship in terms of the weight fraction of each monomer and the respective Tg's of each homopolymer:
1
/Tg
(copolymer)=
w
1
/Tg
1
+w
2
/Tg
2
U.S. Pat. No. 4,754,008, to Siol et al. discloses copolymers of a-methyl styrene and methyl methacrylate (MMA) with a Tg in the range of 130° C. to 150° C. prepared using this approach. Although these copolymers exhibit a very high Tg, they are somewhat difficult to produce due to conversion rate limitations, which require very specific production methods.
Another approach that has been employed to achieve high Tg acrylate ester polymers is the co-polymerization of N-substituted maleimides to stiffen the backbone of the polymer chain, as disclosed in U.S. Pat. No. 5,073,615, to Shen et al. This results in high Tg polymers but is of limited utility because of the low co-polymerization constants of typical maleimides (e.g., N-phenyl maleimide having copolymerizaton constants with MMA of rl
MMA
=1.014; r2=0.164). Considering these values, a feed ratio of almost 30 mol % of the maleimide would be required to obtain a copolymer with 5.0 mol % N-phenyl maleimide in the polymer chain. As a consequence of this and the fact that maleimides will not homopolymerize, large amounts of unreacted N-substituted maleimides would be expected to remain at the end of the polymerization.
Nevertheless, U.S. Pat. No. 5,328,962, to Shen et al., discloses blending a high heat resistant acrylic polymer that is a copolymer of methyl methacrylate (MMA) with N-alkyl-substituted maleimides, with PMMA to yield clear materials having good optical transmittance and an elevated softening temperature. The blends may also incorporate conventional impact modifiers to yield clear samples having superior impact strength compared to normal PMMA. Shen's examples exhibited a single Tg and were clear with little or no haze. However, as indicated above, preparation of the copolymers incorporating N-substituted maleimides presents certain problems in obtaining materials with low residual maleimide content.
Accordingly, a need has continued to exist for a thermoplastic material having the clarity, weather-resistance, and good processing characteristics of PMMA but having a higher heat distortion temperature.
SUMMARY OF THE INVENTION
The problem of providing an acrylate ester polymer having excellent optical and weather resistant properties together with a relatively high heat distortion temperature has now been alleviated by the polymer blends of this invention comprising
1) from about 95% by weight to about 50% by weight of a poly(methyl methacrylate) based polymer comprising
(a) from about 80% by weight to 100% by weight of methyl methacrylate, and
(b) from about 0% by weight to about 20 weight % of a copolymerizable free-radical polymerizable comonomer,
2) from about 5% by weight to about 50% by weight of a copolymer prepared by polymerizing a monomer mixture comprising
(a)from about 50% by weight to about 95% by weight of methyl methacrylate,
(b) from about 5% by weight to about 30% by weight of t-butyl methacrylate, and
(c) from about 0% by weight to about 20% by weight of a copolymerizable lower (meth)acrylate ester monomer; and
preparing a pyrolyzed copolymer by pyrolyzing the resulting copolymer at a temperature of from about 150° C. to about 320° C. for a period of from about 10 seconds to about 10 hours, said pyrolyzed copolymer having a refractive index compatible with that of said poly(methyl methacrylate based copolymer;
3) from about 0% by weight to about 50% by weight of an refractive index compatible impact modifier polymer material.
from about 95% by weight to about 50% by weight of a poly(methyl methacrylate) based polymer comprising
from about 80 weight % methyl methacrylate and
from about 0% by weight to about 20 weight % of copolymerizable free-radical polymerizable comonomer,
from about 5% by weight to about 50% by weight of a copolymer prepared by polymerizing a monomer mixture
Accordingly, it is an object of the invention to provide a blend of acrylic ester polymers and/or copolymers.
A further object is to provide a blend of acrylic ester polymers and/or copolymers having a high heat distortion temperature.
A further object is to provide a blend of acrylic ester polymers and/or copolymers having a high glass transition temperature (Tg).
A further object is to provide a blend of acrylic ester polymers and/or copolymers having a heat distortion temperature higher than that of a poly(methyl methacrylate) polymer.
A further object is to provide a blend of acrylic ester polymers and/or copolymers having a glass transition temperature (Tg) higher than that of a poly(methyl methacrylate) polymer.
A further object is to provide a copolymer of methyl methacrylate and t-butyl methacrylate.
A further object is to provide a copolymer of methyl methacrylate and t-butyl methacrylate that has been pyrolyzed to provide a copolymer having an increased glass transition temperature.
A further object is to provide an acrylic ester copolymer that can be blended with poly(methyl methacrylate) to provide a clear plastic material having an increased heat distortion temperature.
A further object is to provide a copolymer of methyl methacrylate and t-butyl methacrylate that has been pyrolyzed to provide a copolymer having an increased glass transition temperature.
A further object is to provide a copolymer of methyl methacrylate and t-butyl methacrylate that has been pyrolyzed to provide a copolymer having an increased glass transition temperature and can be blended with poly(methyl methacrylate) to provide a clear plastic material having an increased heat distortion temperature.
Further objects of the invention will be apparent from the description of the invention which follows.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
Acc
Chan David T.
Faris Tom V.
Gordon Greg T.
Boland Thomas R.
Connolly Bove & Lodge & Hutz LLP
Nutter Nathan M.
Plaskolite Inc.
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