(Ethylene, vinyl acetal) copolymers and their use in lithographic printing plate precursors

1. A copolymer comprising:

a plurality of ethylenic moieties A having a structure according to the formula:

wherein

R 2 and R 3 independently represent hydrogen;

a plurality of acetal moieties B having a structure according to the formula:

wherein

L 1 is a divalent linking group;

X=0 or 1;

R 1 represents an optionally substituted aromatic or heteroaromatic group including at least one hydroxyl group; and

a plurality of acetal moieties C and/or a plurality of acetal moieties D that include a structural moiety including a chromophoric group having a main absorption in the infrared region.

2. The copolymer according to claim 1 , wherein the plurality of acetal moieties C and/or the plurality of acetal moieties D have a structure according to the formulae:

wherein

L 2 and L 3 independently represent a divalent linking group;

y and z independently represent 0 or 1; and

R 4 and R 5 independently represent a structural moiety including a chromophoric group having a main absorption in the infrared region.

3. The copolymer according to claim 1 , wherein the plurality of acetal moieties C have a structure according to the formula:

wherein

R6 represents a structural moiety including a chromophoric group having a main absorption in the infrared region and a bond to the center of the aromatic ring indicates that any of the hydrogen atoms of the aromatic ring may be substituted by —O—R6.

4. The copolymer according according to claim 1 , wherein the chromophoric group has a structure according to the formula:

wherein

T and T′ independently represent one or more substituents or an annulated ring;

Z and Z′ independently represent —O—, —S—, —CR e R f —, or —CH═CH— and wherein R e and R f independently represent an optionally substituted alkyl or aryl group;

R z and R z′ independently represent an optionally substituted alkyl group;

R b and R c independently represent a hydrogen atom, an optionally substituted alkyl group, or atoms necessary to form an optionally substituted ring structure;

R a and R d independently represent a hydrogen atom or an optionally substituted alkyl group;

R z and R a or R d and R z′ may represent atoms necessary to form an optionally substituted 5- or 6-membered ring;

X − renders the chromophoric group neutral; and

* denotes a linking position.

5. The copolymer according to claim 2 , wherein the copolymer comprises the plurality of acetal moieties C.

6. The copolymer according to claim 1 , which is represented by the formula:

wherein

R 1 represents an optionally substituted aromatic or heteroaromatic group including at least one hydroxyl group;

R 4 represents a structural moiety including a chromophoric group having a main absorption in the infrared region;

R 7 is an optionally substituted alkyl group;

L 2 represents a divalent linking group;

m is in a range of 10 to 55 mol %;

n is in a range of 15 to 60 mol %;

o is in a range of 10 to 60 mol %;

p is in a range of 0 to 10 mol %;

q is in a range of 0.25 to 25 mol %; and

y represents 0 or 1.

7. A positive-working lithographic printing plate precursor comprising:

a support including a hydrophilic surface or which is provided with a hydrophilic layer; and

a heat- and/or light-sensitive coating provided on the support; wherein

the coating includes the copolymer as defined in claim 1 .

8. A method of making a lithographic printing plate precursor comprising the steps of:

providing a support with a hydrophilic surface or with a hydrophilic layer;

applying a coating including the copolymer as defined in claim 1 on the support or on the hydrophilic layer; and

drying the precursor.

9. A method of making a lithographic printing plate comprising the steps of:

providing a lithographic printing plate precursor according to claim 7 ;

image-wise exposing the lithographic printing plate precursor with heat and/or light; and

developing the lithographic printing plate precursor by treating the lithographic printing plate precursor with a developing solution to remove exposed areas of the coating from the support or the hydrophilic layer.