Process for producing thermoplastic polymer compositions with optimized degree of crosslinking
A process produces a polymer composition (A) containing a styrene copolymer (a) and an impact modifier (b), comprising a copolymer (b1) as graft base and a graft (b2), where the steps of the process are: (1) providing a crosslinked copolymer (b1) made of: (b11) from 70 to 99.99% by weight of a conjugated diene or acrylate, (b12) from 0 to 29% by weight of another comonomer, (b13) from 0 to 10% by weight of crosslinking monomers, and (b14) from 0.01 to 0.7% by weight of a chain-transfer reagent; (2) applying, to the copolymer (b1), at least one graft (b2) comprising: (b21) from 65 to 95% by weight of a vinylaromatic monomer, (b22) from 5 to 35% by weight of acrylonitrile and/or methacrylonitrile, and (b23) from 0 to 30% by weight of monoethylenically unsaturated monomers, thus providing the impact modifier (b); (3) mixing the styrene copolymer (a) and the impact modifier (b), and thus leads to improved mechanical properties of the polymer composition (A).
1. A process for optimizing the degree of crosslinking (V) of a crosslinked copolymer (b1) until a desired degree of crosslinking (V′) is obtained for a crosslinked copolymer (b1′) as graft substrate for a polymeric impact modifier (b), wherein said copolymers (b1) and (b1′), independently of one another, are produced from a monomer mixture comprising:
(b11): 70 to 99.99 wt % of at least one conjugated diene and/or of at least one acrylate,
(b12): 0 to 29 wt % of at least one further comonomer selected from: styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, and methyl methacrylate,
(b13): 0 to 10 wt % of one or more polyfunctional crosslinking monomers, and
(b14): 0.01 to 0.7 wt % of a chain transfer agent,
based on the entire monomer quantity of the polymerization mixture for producing said copolymer (b1) or (b1′);
wherein the process comprises the steps of:
(i) polymerizing the monomer mixture for producing said copolymer (b1);
(ii) determining via NMR relaxation measurements the degree of crosslinking (V) of said copolymer (b1) obtained in step (i);
(iii) polymerizing a modified monomer mixture to produce a modified copolymer (b1′), wherein the parameters of the polymerization reaction are adapted according to said crosslinking (V) determined as per step (ii) for said copolymer (b1) and according to the desired crosslinking (V′) of said copolymer (b1′) as graft substrate as determined via NMR relaxation measurements; and
(iv) repeating said steps (i) to (iii) as often as necessary until a desired degree of crosslinking (V′) is obtained for said crosslinked copolymer (b1′) as graft substrate for said polymeric impact modifier (b), and wherein
the transversal relaxation time T2 is used to determine said degree of crosslinking (V) and (V′) of said copolymers (b1) and (b1′),
said degree of crosslinking (V) and (V′) of said copolymers (b1) and (b1′) is determined by using a low-field NMR spectrometer at a field strength ranging from 0.001 to 1.5 teslas, and
the desired degree of crosslinking (V′) for said crosslinked copolymer (b1′) as graft substrate for said polymeric impact modifier (b) ranges from 2.0 to 7 ms T2 times, as measured on filmed samples at 140° C.
2. The process as claimed in claim 1 , characterized in that the step of providing said copolymer (b1′) according to said degree of crosslinking (V) determined in step (ii) for said copolymer (b1) resulting from the first polymerization reaction is carried out by admixing the reaction mixture of the polymerization mixture as per step (iii) additionally with a polyfunctional crosslinking monomer (b13) as crosslinking agent and/or a chain transfer agent (b14), or changing the reaction temperature in the polymerization reaction, or a combination thereof.
3. The process as claimed in claim 1 , characterized in that the step of providing said copolymer (b1′) is carried out by subjecting the reaction mixture of the polymerization reaction to a temperature change by not less than 10° C.
4. The process as claimed in claim 1 , characterized in that the reaction mixture has added to it a chain transfer agent in an amount of 0.1 to 0.6 wt %, based on the entire monomer quantity of the polymerization mixture for producing said copolymer (b1′).
5. A method of using the process as claimed in claim 1 in the manufacture of a copolymer (b1′) having an optimized degree of crosslinking (V′) as graft substrate for said polymeric impact modifier (b).
6. The process as claimed in claim 1 , wherein the degree of crosslinking (V) and (V′) of said copolymers (b1) and (b1′) is determined by using a low-field NMR spectrometer at a field strength ranging from 0.1 to 0.6 tesla.