NOVELTY - Preparing a rubber precursor or a rubber composition comprising modified inorganic oxygen-containing particulate material involves preparing mixture of the modified particulate material and a first solvent; contacting the mixture with a rubber precursor containing polymer and optionally a second solvent, or contacting the mixture with a monomer composition containing monomer and optionally a second solvent, and polymerizing the monomer to form the rubber precursor; and optionally cross-linking the rubber precursor in the presence of a cross-linking agent.    USE - For preparing rubber precursor and rubber composition used in solar cell units and masterbatch (claimed). Also useful in tyre such as car tyres, truck tyres, off-the-road tyres and aircraft tires; in latex products including gloves, condoms, balloons, catheters, latex thread, foam, carpet backings and rubberized coir and hair; in footwear; in civil engineering products such as bridge bearings, rubber-metal-laminated bearings; in belting and hoses; in non-tire automotive applications including engine mounts, rubber bearings, seals, grommets; in wires and cables; and in pipe seals, medical closures, rollers; rubber balls and tubing; milking inflations; and other agricultural-based applications.    ADVANTAGE - The modified particulate material disperses in the rubber precursor without agglomeration compared to conventional processes and thus economical; has a good compatibility with resins; enables a reduction of the total amount of inorganic filler in the rubber composition and maintains similar or improved mechanical properties. The mixture of the modified particulate material and the first solvent can be easily handled, has a relatively low viscosity, and enables easy mixing into the rubber precursor. During the process of the first solvent is evaporate largely or even completely without using a separate evaporation step, and without void formation in the final rubber composition. The process provides the rubber composition with improved mechanical properties such as durometer hardness, tensile strength, elongation, modulus, tear strength, and improved optical properties. The rubber composition have transparency to visible light, which enables application at a position where light travels through the rubber composition before the light reaches the part of the cell where the light is converted into electrical energy.    DETAILED DESCRIPTION - Preparing a rubber precursor or a rubber composition comprising modified inorganic oxygen-containing particulate material involves: (a1) preparing a mixture of the modified particulate material and a first solvent; (b) contacting the mixture with a rubber precursor containing at least one polymer and optionally a second solvent, or contacting the mixture with a monomer composition containing at least one monomer and optionally a second solvent, and polymerizing the monomer(s) to form the rubber precursor; (c) optionally cross-linking the rubber precursor in the presence of a cross-linking agent to form a rubber composition; and (d) optionally removing the first and/or second solvents.    INDEPENDENT CLAIMS are included for the following:    (1) rubber composition obtainable by the process comprising rubber and the particulate material modified with a coupling agent, where the particulate material has a dimension of 1-1000 nm in at least one direction;    (2) masterbatch obtainable by the process comprising the rubber precursor (20-95 wt.%) and the particulate material (5-80 wt.%) having a dimension of 1-1000 nm in at least one direction, where the particulate material is modified with a coupling agent; and    (3) solar cell unit comprising a layered structure containing a back electrode, photovoltaic layer, front electrode, transparent top layer and a layer of the rubber composition between the front electrode and the transparent top layer, where the rubber is a transparent rubber composition (preferably a silicone rubber).